This is something that has been an issue for as long as I can remember, but I didn't find an actual bug report on it. The LFG tool lists games as currently having one more player than is accurate. Perhaps the GM is included in the total here, but not on the actual game page? Regardless, as a consequence, the number of open slots shown is one lower than is accurate. This is particularly troublesome for games looking for just one more player, as the tool considers the game full and therefore doesn't show the listing at all.